1. Field of the Invention
The present invention relates to a method of manufacturing a lens for making an optical display by means of an optical imager designed to allow access to information through optical projection of a digital image, for example of multimedia type or data type, for example GPS data.
2. Description of Related Art
The term “lens” is used herein to designate an optical system suitable in particular for being positioned in a frame for spectacles or eyeglasses. This term “lens” is used herein to mean a finished lens ready for placing on a spectacles frame, or an unfinished lens or lens blank, i.e. which still needs to be cut by trimming, surfacing and polishing, in order to be usable.
Patent document WO 01/95027 discloses a projection insert constituted by an optical imager for forming the light beams coming from an electronic and optical system for generating light beams based on an electronic signal, the system being of the miniature screen, laser diodes, or light-emitting diodes (LED) type. The optical imager directs the light beams towards the wearer's eye to enable the information content to be viewed, as a virtual image.
This prior art optical imager includes a light-transmitting mineral, substrate, specially made of glass, a wave-reflecting substrate surface carried by the substrate for coupling light from a entry surface into the substrate by total reflection and a plurality of partially reflecting surfaces carried by the substrate and parallel to each other and not parallel to any of the edges of the substrate in order to direct the light beams towards the wearer's eye.
Because this type of display enables an optical imager to be obtained of small thickness, especially of around 2 mm or lower, it achieves a compromise between the display function and the vision correction function. The faces of the lens can be involve in both functions, so for example it is possible to change the radius of curvature of one face for vision-correction reasons without disturbing the display function.
The patent document WO 2006/016086 proposes a method of manufacturing an optical display that can also correct the vision of a user, while being mass-produced in reliable manner, by decoupling the display and the vision-correction functions.
To this end, this patent document provides a method of manufacturing a vision-correction lens that has a front face and a rear face, and into which light beams emitted by an optical light beam generator system are introduced via an entry surface and directed towards the eye of the wearer to enable information content to be viewed, said light beams being reflected a plurality of times between two reflection faces, between being introduced into the lens and exiting therefrom, said two reflection faces being faces of a transparent optical insert constituted by a light guide.
This insert is completely contained within the lens by placed it in the lens blank while it is being molded in a mold comprising a first mold portion for molding the front face, and a second mold portion for molding the rear face and a monomer is casted into this mold, in order to obtain a circular lens blank which is then treated by surfacing and polishing and cut by trimming to the form of the finished lens ready for placing on a spectacles frame.
According to this known process, the insert is rectangular, with for example a length of 43 mm and a width of 20 mm. Consequently, its surface is smaller than the cut total surface of the final lens.
Such method raises the following technical problem. Because of the mechanical solicitations created between the glass of the insert and the monomer of the lens blank during the heated casting of the monomer and revealed by the mechanical efforts resulting from the surfacing and the polishing of the lens blank, it appears an optical defect in the vicinity of the edges of the insert. This defect gives a loss of the qualities of transmission of the lens and a variation of the optical powers in these zones.
In order to solve this problem, it can be consider an insert which presents a surface greater that the surface of the final lens and after placing of the monomer constituting the lens blank, the final lens can be cut by trimming at its dimension.
The patent document EP 1 748 305 proposes such process where the surface of the final insert is equal to the surface of the final lens, the insert being a plane substrate stacked in close contact between two other plane substrates serving a function of diopter correction of the viewing eye, one disposed on the external side and one disposed on the viewer side.
In order to manufacture such optical display, an blank insert having for example a length of 57 mm and a width of 35 mm and two blank plane substrates with the same surface dimension are stacked with the insert, surfaced, polished and cut by trimming to the form of the finished lens ready for placing on a spectacles frame. Such method gives an insert extending on all the surface of the final lens.
Such method raises the following technical problem. The cutting has to be done inside a width which comprises two materials, glass for the insert and plastic material for the two plane substrates. These two materials have a very different hardness and the cutting by trimming is very difficult to do, causing separation, break or splitting of the materials.